The present invention relates to a fuel injection valve for use in an internal combustion engine. More particularly, the present invention relates to a structure for ensuring a correct fuel injection quantity by minimizing the water hammer action of fuel pressure occurring in the fuel injection valve.
A direct-injection engine in which high-pressure fuel is injected directly into the combustion chamber of the engine from a fuel injection valve is known. In such a direct-injection engine, stratified combustion is used during low-load conditions. The stratified combustion uses an air/fuel charge consisting mainly of a lean mixture and a small layer of rich mixture localized in the vicinities of the ignition plug to improve ignitability. In the stratified combustion, the fuel is injected into the combustion chamber during the compression stroke. In other words, the fuel is injected when the pressure in the combustion chamber is high. Accordingly, the pressure of fuel sent to the fuel injection valve is extremely higher than in the case of the conventional intake-manifold injection engines. That is, the pressure of fuel when injected is about 20 Mpa. When the needle valve is fully closed to stop the fuel injection, the pressure of fuel is as high as about 80 Mpa.
Accordingly, as shown in FIG. 7, when a fuel injection valve 21 shifts from a position in which a needle valve 14 is fully open to perform fuel injection to a position in which the needle valve 14 is fully closed to stop the fuel injection, a water hammer action occurs in the fuel injection valve 21 as a result of the sudden closing of the needle valve 14. This produces a high-pressure wave that goes upstream in the fuel injection valve 21 and acts on the distal end surface 13a of an armature 13 in such a manner as to lift the armature 13, causing the needle valve 14 to move in the direction in which it opens. That is, a bouncing phenomenon occurs. As shown in FIG. 6, the bouncing phenomenon includes a primary bounce (shown by A in the figure), a secondary bounce (shown by B in the figure) and a tertiary bounce (shown by C in the figure), which occur successively. Then, the bouncing phenomenon gradually attenuates to subside. During the bouncing phenomenon, fuel is undesirably discharged when the needle valve 14 opens. Therefore, the amount of fuel discharged in the total period of time that the needle valve 14 is open is added to a predetermined fuel discharge quantity. Accordingly, the total fuel discharge quantity becomes slightly larger than a predetermined value. This causes waste of fuel and variations in the air-fuel ratio.
Accordingly, an object of the present invention is to provide a fuel injection valve capable of minimizing the waste of fuel and variations in the air-fuel ratio by damping the high-pressure wave produced by the water hammer action and thus suppressing the occurrence of the bouncing phenomenon.
To attain the above-described object, the present invention provides a fuel injection valve wherein a needle valve integrally secured to an armature is lifted by excitation of an electromagnetic coil to inject fuel into a combustion chamber from an injection hole formed in a nozzle. In the fuel injection valve, a water hammer absorbing member is provided between the armature and the injection hole to absorb a water hammer pressure wave produced by sudden closing of the needle valve.
The water hammer absorbing member may be a metallic sheet formed in the shape of a polygonal cylinder having a fin at each vertex thereof.
The water hammer absorbing member may be a metallic mesh wound a plurality of turns into a circular cylinder.
The water hammer absorbing member may be a synthetic rubber formed in the shape of a circular cylinder.
The water hammer absorbing member may be a spongy elastic material formed in the shape of a circular cylinder.
In addition, the present invention provides a fuel injection valve having an injection hole formed at the distal end of a nozzle secured to a body and a valve portion formed at the distal end of a needle valve secured to an armature. The valve portion of the needle valve is urged toward the injection hole by resilient force exerted by a spring. The valve portion of the needle valve is lifted away from the injection hole by magnetic force produced by an electromagnetic coil. In the fuel injection valve, an annular plate is sandwiched between the body and the nozzle to define a space in the nozzle. Further, a water hammer absorbing member for absorbing a water hammer pressure wave is fitted in the space in the nozzle in such a manner that the water hammer absorbing member is kept out of contact with the needle valve.
With the above-described arrangement, the present invention provides the following advantageous effects.
A high-pressure wave produced by a water hammer action is absorbed and damped by the water hammer absorbing member. Therefore, it is possible to reduce the pressure wave propagated to the armature and hence possible to reduce the amount of lift of the needle valve due to a bouncing phenomenon. Accordingly, the amount of fuel excessively discharged is reduced. Thus, it becomes possible to minimize the waste of fuel and variations in the air-fuel ratio.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.